In personal mobile communication, since the power available for a user equipment (UE) is very limited, it is a critical problem to save the UE power as much as possible in order to extend the stand-by time of UE. Currently, a widely recognized method of effectively reducing the UE power consumption is to adopt Discontinuous Receiving (DRX) technology, i.e. to make UE periodically close its receiving unit so as to enter Idle mode. This method is remarkably effective for saving power.
A necessary procedure for converting the UE from Idle mode into Active mode is Paging Procedure. This procedure is implemented via paging control channel (PCCH), paging channel (PCH), secondary common control physical channel (S-CCPCH) and paging indicator channel (PICH) in WCDMA. In idle mode, the UE needs to complete periodical supervision procedure in order to monitor paging channel; once receiving paging information related to the UE itself, the UE is converted into active mode and receives the paging from the network. The above-mentioned monitoring in periodical supervision procedure is realized through monitoring paging indicator. The paging indicator is sent once via paging indicator channel (PICH) in every cycle. If on the PICH, the identification bit corresponding to the paging group to which the UE belongs is set as 1, the UE decodes the paging channel immediately coming in the next slot; if the identification bit is 0, then the UE immediately returns to sleep mode, which significantly decreases the power consumption of power supply.
Therefore, the using of the paging indicator channel (PICH) becomes the crux for effectively improving the performance of the paging procedure in the UMTS terrestrial radio access network (UTRAN) of universal mobile telecommunication system (UMTS).
As a non-directional, point-to-multipoint bearing transmission mode within a cell, multimedia broadcast/multicast services (MBMS) has drawn more and more attention with the development of 3G mobile communication. This mode transmits data from a single source entity to multiple sink receiving points, and moreover, its advanced function of data distribution raises the utilization efficiency of wireless sources to a maximum. In addition, compared with the original multicast services in wireless communication, this mode effectively improves the utilization ratio of wireless bandwidth since it supports higher transmission rates.
Like conventional services, MBMS also requires the service notification procedure which is similar to the paging operation. After the “Session” starts, the notification procedure will notify the UE of MBMS data transferring which is currently and about to be conducted. Likewise, the task that the UE periodically monitors the notification procedure is performed through monitoring the notification indicator (NI). In order to differentiate common paging indicator channel (PICH), the channel bearing NI is marked as the notification indicator channel (MICH).
Like the PICH and PI, the basic object of realizing the MICH and NI is to save the consumption of UE's power supply as much as possible. To achieve this object, it is necessary to transmit NI to each UE precisely and rapidly. However, in the prior art, only in the c/sh/m sub-layer of the Media Access Control (MAC) layer in the Radio Network Controller (RNC) are provided queues for sequencing paging messages, whereas a corresponding control mechanism with respect to notification messages and notification indicator is still lacking.
In a conventional Paging Procedure, the RNC first divides all UEs into groups. The numbers of groups allowable under the protocols are 18, 36, 72 and 144, corresponding to 18, 36, 72 and 144 PI values. A concrete way of grouping is as illustrated by expression (1):PI={IMSI div 8192} mod Np  (1)wherein Np is the number of groups divided, which may be one of 18, 36, 72 and 144; IMSI denotes an international mobile subscriber identifier, for identifying a GSM subscriber; div denotes division operation, and mod denotes modulus operation.
As seen from expression (1), the RNC finishes grouping UEs after such calculation, that is, the value of PI indicates which paging group the UE is assigned to. This means that PI of a certain UE must be an integer from 0 to Np−1.
The international mobile subscriber identifier (IMSI) defined in the Rel-99 is used for identifying a GSM subscriber, the format of which is as shown in FIG. 1. In the figure, the MCC indicates the country which the UE belongs to, having a length of 3 decimal digits; the MNC indicates the network range which the UE falls into, having a length of 2-3 decimal digits; the MSIN is the identification number of the UE per se, having a length of 9-10 decimal digits; thus, the IMSI has a total length of 15 decimal digits.
It should be pointed out that, the notification procedure in MBMS is directed to services other than the UE per se, and hence, the grouping procedure is also aimed at services. The principle of grouping in notification is the same as that during the Paging Procedure, and the only difference is that the MSIN in FIG. 1 is replaced by MBMS service Ids. The MCC, MNC and MBMS service Ids are termed TMGI as a whole, and then, the grouping method during the notification procedure of MBMS is as illustrated by expression (2):NI=TMGI mod Mn  (2 )where the TMGI is a decimal digit formed by MCC, MNC and MBMS service Ids, and Mn is available maximum number of groups of MBMS to be divided.
Thus, different from the original paging, the Notification Procedure is directed to services other than the UE per se. Consequently, false alarm with respect to a certain or several services, if there any, will lead to unnecessary power consumption of numerous subscribers of the service(s). Therefore, there is a need to increase the maximum dimension Mn as much as possible so as to accordingly reduce the service number of each divided group as much as possible. Of course, it is impossible to reduce this number unlimitedly, because with the growing increase of future MBMS services, this number is also allowed to increase properly on condition that the performance of false alarm is not impaired.
In general, NI is loaded in a radio frame of the MICH. There are three existing designing methods with respect to the MICH frame structure:
1) MICH Multi-map Structure
In PICH structure design as defined in the Rel-99, each PI is mapped to its PI bitmap and to the number of group divided Np in PICH, respectively. Thereby, the maximum number of groups divided by PI is equal to the maximum value of grouping, i.e. 144. However, in the future third-generation (3G) mobile communication, there might be tens of or even hundreds of thousands of MBMS services in each cell. Thus, the maximum dimension Mn of grouping MBMS services is far from enough if it is merely maintained at the level of the existing number Np of grouping.
To this end, 3GPP TSG RAN WG2 Meeting #39, R 2-032608, MBMS Common paging with 1 UE DRX cycle, Source: Samsung and 3GPP TSG RAN WG2 MBMS Adhoc Meeting, R2-040758, Reducing the false alarm probability on MICH decoding proposes an implementation method of using a plurality of original locations of group identification to express NI of one MBMS service in the MICH. As shown in FIG. 2, suppose there are 4 groups divided in the original MICH, i.e. Np=4. With the method of one-to-one mapping, the maximum range for the maximum dimension Mn is 4, that is, only 4 MBMS groups can be divided into. However, with the method of one-to-two mapping, the maximum dimension Mn will reach a maximum range of 6. In this way, the value range of the maximum dimension Mn widens.
Referring to FIG. 2, suppose the original mapped location number of the MICH is Np and the map number adopted is m, then the obtained Mn is as illustrated by expression (3):
                              M          n                =                              C                          N              p                        m                    =                                                    N                p                            !                                                      m                !                            ·                                                (                                                            N                      p                                        -                    m                                    )                                !                                                                        (        3        )            
That is to say, Mn equals to the combination of m from the mapped location number Np.
There is no doubt that the adopting of such a multi-map way can increase categories of divided groups of MBMS services. The false alarm performance is as shown in 3GPP TSG RAN WG2 MBMS Adhoc Meeting, R2-040758, Reducing the false alarm probability on MICH decoding. Thus, if two NIs, i.e. NI1 and NI2, fall into the same MBMS group, the radio frame structure of the MICH is as shown in FIG. 3. It can be seen from FIG. 3 that, since the two NI fall into the same group, the identifiers of their NIs in plural MICH frames completely coincide and then false alarm arises.
To sum up, the multi-map way has the following characteristics:
A notable advantage of the MICH map way lies in the capability of effectively expanding the mapping range of MBMS groups within one MICH radio frame. Therefore, it is of practical significance to decrease the UE false alarm ratio and reduce the UE power consumption.
On the other hand, a tangible disadvantage of the MICH map way lies in being not conducive to transmission of plural NIs in one MICH radio frame. As is clear from FIG. 2, the most unfavorable situation is that if two NIs needs to be mapped to the first map mode and the sixth map mode on the right-hand side of the figure, then all of PI1, PI2, PI3 and PI4 in the entire MICH have mapping. Here, six possible modes all exist, i.e., new false alarm and error detection crops up. As a result, the grouping performance declines greatly.
The MICH map way trades the MICH wireless transmission performance for the advantage of false alarm ratio in MBMS grouping. Since the inspection and decision of the map way require simultaneous correct decision of a plurality of map bits, the overall MICH wireless transmission performance is somewhat abated.
2) MBMS Grouping Decision of a Plurality of Radio Frames
Based on the existing PICH scheme, as known from the above, there are two good ways to effectively reduce the false alarm ratio: one is to increase the value range of the maximal dimension Mn and the other is to improve the MICH power consumption. They reflect the two sides of this problem. The solution scheme of the present method is to impose new restrictions on the time axis, which can be realized through defining a random sequence which is in a number much greater than the grouping number Np. In this way, the possibility that two different MBMS services completely overlap with each other in an entire notification interval is lowered significantly. In other words, the UE reduces its own false alarm probability through reading more MICH radio frames in the notification cycle. A more extreme situation is that a user who receives MBMS services on his initiative will keep reading the MICH until he identifies correctly the service, in which case the false alarm probability is 0 theoretically. The simplest way to define the random sequence is to generate a pseudo-random (PN) sequence via a shift register. Different MBMS services use different seeds of the register so as to be located in different locations of the sequence.
Thus, if two different NIs, namely NI1 and NI2, fall into one identical notification interval, then their locations in the MICH are as shown in FIG. 4. As is clear from FIG. 4, although NI1 and NI2 have the same identification location in the first frame, they can be separated from each other through reading subsequent frame(s), so that the false alarm ratio is reduced.
In a word, the method has distinct properties which are summarized as follows:
This grouping scheme produces effective results for improving the UE false alarm ratio performance. As seen from protocols, a number of MICH frames will be sent in one notification adjustment period. If one frame is divided into Np groups, then the total number Mn of divided groups for k MICH frames is (Np)k. For example, take Np=18 as a typical value, when k≧3, Mn will reach a fairly large value.
Like the first scheme, when multiple NIs are needed in a sequence, this grouping method will generate additional false alarm(s); when each MICH frame contains multiple NIs, the UE cannot set up one-to-one corresponding sequence relation for different NIs in different MICH frames, and thereby, more additional alarms are inevitable.
Similarly, the overall wireless transmission performance of MICH for this grouping method is also affected to a different degree. Since in the original PICH, the UE needs to decode correctly one PI symbol only; however, the current UE needs to decode continuously and correctly k symbols in the MICH. So the overall receiving performance is affected to some degree. It is more important that, due to real-time change of wireless transmission conditions among different MICH frames, the transmission performances are different or even varies considerably. Therefore, the overall decision performance is also subject to more serious influence.
The largest deficiency of this method lies in the long duration for the UE to read the MICH. To identify whether the MICH contains NIs of MBMS services subscribed for itself, each UE needs to read several MICH radio frames. Thus, the UE power consumption is increased, making it impractical in engineering practices.
3) Discontinuous Arrangement of Modulating Bit in the MICH
This scheme mainly focuses on the mapping relation between NI symbols and modulating bit in the MICH. In the Rel-99, a modulating bit corresponding to each PI symbol is continuous. Thus, if this mechanism goes on, the structures of the PICH and the MICH are as shown in FIG. 5.
As seen from FIG. 5, suppose the UE is in idle mode, then the UE will awake in a paging occasion belonging to a specific UE within every DRX cycle, so as to monitor PI segment belonging to itself on the PICH. Since the protocol prescribes that there is no specific paging occasion in the MICH design of MBMS, the MICH reading will resort to paging occasion when the UE is in idle mode. Since the UE-based PI (relevant to subscriber identifier) and MBMS services-based NI (relevant to services identifier) are totally irrelevant to each other, the corresponding PI segment and NI segment probably will not be superposed. In view of this, the duration for the UE to read the indicator channel is lengthened. The most unfavorable situation is that maybe the UE need to read indicator channel information as long as 10 ms.
3GPP TSG RAN WG1 Ad-hoc, R1-040088, MBMS PICH and 3GPP TSG RAN1 #37b (Rel-6 AH), R1-040713, Discussion and proposal for MICH coding and mapping puts forward a method of discontinuous arrangement of PI modulating bit, which is as shown in FIG. 6.
In the method as illustrated in FIG. 6, several identical segments are reproduced from NI according to the bit number of PI and then distributed to each sub-frame, respectively. These sub-frames are obtained through evenly segmenting the entire PICH frame. Thereby, no matter when PI awakens the UE for monitoring, it is guaranteed that one sub-segment of NI can be monitored while the UE is awake, so that the notification indicator is obtained.
What needs to be pointed out is that the present method does not change the grouping number Np of NI load in the MICH. A fundamental object of this method is to reduce the average awaking time of the UE. The essence of the method is to segment and reproduce the original NI modulating bit sets in the MICH. The concrete number of segments D is defined by the following expression:
                    D        =                              ⌊                                          288                /                                  N                  n                                                            288                /                                  N                  p                                                      ⌋                    =                      ⌊                                          N                p                                            N                n                                      ⌋                                              (        4        )            wherein Np is PI grouping number in the PICH, and Nn is NI grouping number in the MICH.
NI of the MICH in FIG. 5 is divided into D equal segments as illustrated in expression (4), which are then re-placed in the entire MICH as shown in FIG. 6. Thus, NI information is read while the UE awakes and reads PI information in a paging occasion in every DRX cycle. Obviously, the average paging time span for the UE in FIG. 6 is greatly less than the UE average paging time in FIG. 5, which is theoretically equal to 1/D of the original average paging time. According to expression (4), PI and NI obtain a same number of modulating bits in a paging period, and thereby, they have equivalent wireless interface transmission performance. Another major reason accounting for the effectiveness of this method is that, both the PICH and the MICH are common transport channels, not only their transmission power can be received by all UEs in a cell, but also it is unnecessary for most UEs to receive all energy of PI. So to split bit string under this regime is workable.
In summary, this method has the following advantages and disadvantages:
The method effectively reduces the average reading time of the PICH and the MICH for the UE in an idle state. This property decreases the UE power consumption from another perspective, since the method causes irrelevant UE to rapidly return to idle state from a state of monitoring the paging channel.
As in this method, the mapping relation between NI and the grouping number Np in the MICH does not change substantively, this method allows NIs of a plurality of MBMS to coexist in one identical MICH frame without causing additional false alarm ratio.
However, the gravest disadvantage of this method is that the grouping number Mn of MBMS service identification is too small, which is merely equal to the original grouping number Np. Consequently, this method fails to meet requirements of the possible number of MBMS services in a cell. Therefore, if the method is employed directly, serious UE false alarm ratio will be produced and the UE power is over-consumed.
On the other hand, with respect to MBMS, two main resources, namely channelisation code and transmission power, are required so as to realize transmission. Like the conventional PICH, the MICH also requires a channelisation code with a spreading factor equaling 256. In addition, to meet certain false alarm ratio, the MICH further needs a transmission power which is much higher than the data channel. Since the modulation mode for the conventional PICH is phase shift keying (QPSK), it is possible to perform modulation combining the PICH and the MICH using the QPSK mode, so that the two types of indicator channels can realize downlink transmission using only one SF-256 channelisation code. Such an idea has reached a common understanding in the present 3GPP standardization course. In other words, to save wireless resources as much as possible while maintaining the existing structure at the same time, the MICH can be carried on the PICH to perform transmission using the QPSK modulation mode.
Moreover, both the transmission of physical channels (S-CCPCH) bearing MBMS Control Channel (MCCH) and MBMS Traffic Channel (MTCH) and the MICH should follow the principle of power consumption optimum for selection and design.
To maintain various structures in the prior network as much as possible, joint modulation is performed on the MICH and the PICH. Through taking into comprehensive consideration various states of MBMS notification indicator and the paging indicator in the Rel-99, all possible constellation points on the I-Q plane is obtained as shown in table 1.
TABLE 1all possible constellation points on the I–Q planeConstellationpointspaging indicators in Rel-99MBMS notification indicatorsEONOFFFOFFOFFGONONHOFFON
It can be seen from table 1 that, the states involved in the method of joint modulation on the MICH and the PICH include only four points, namely E, F, G and H.
The initial modulation mode in the prior art is pulse amplitude modulation, which, as shown in A of FIG. 7, properly distributes the four constellation points on the I-Q plane based on difference in amplitude. In order to effectively improve the performance of power consumption and the peak-average ratio of transmission, the QPSK mode as shown in B of FIG. 7 is then adopted. In general, several problems need to be taken into account when designing of modulated constellation points: first of all, the peak-average ratio of transmission power should be as low as possible in order to raise the efficiency of power amplifier as much as possible; next, the Euclidean Distance between adjacent points should be kept minimum as much as possible on the premise of guaranteeing predefined symbol error ration (SER) and bit error ratio (BER); and lastly, the most important thing is to reduce the transmission power of jointly modulated by the MICH and the PICH as much as possible.
As is clear from table 1, the constellation point “F” denotes a state where there is neither the paging indicator nor the notification indicator. For the majority of UEs, this state appears most frequently and lasts for longest in a day, the appearance probability of which is about 88%. Thus, in this modulation method, such a constellation point without any useful information consumes the same transmission power as other constellation points, which causes a considerable waste of constellation point.
Due to the introduction of MBMS, the situation of the Power Limited on downlink in a WCDMA system will deteriorate.